Apply the appropriate transformations described in Section 10.4.2 to the associations of F...

Apply the appropriate transformations described in Section 10.4.2 to the associations of Figure, Assume that all associations are bidirectional and that they can change during the lifetime of each object. Write the source code needed to manage the associations, including class, field, and method declarations, method bodies, and visibility.

Figure: Associations among Messages, Folders, Mailboxes, and Views in a hypothetical E-mail client (UML class diagram).